This invention relates to bearing retainers, cages or separators, and more specifically, to improved lubricating ball bearing retainers employing a soft, flexible oil impregnated material.
Generally, lubricating ball bearing retainers have employed a porous, oil impregnated cotton or paperphenolic laminated material, or the like. Such prior art bearing retainers are shown in U.S. Pat. No. 3,627,607, issued Dec. 14, 1971, for Method of Manufacturing a Bearing Cage, and U.S. Pat. No. 3,529,875, issued Sept. 22, 1970, for Reinforced Lubricating Ball Bearing Cage. These prior art ball bearing retainers exhibit a number of disadvantageous properties. The phenolic laminate material contains contaminants which cause non-wetting of the surfaces of the ball bearings in the bearing races, and non-wetting leads to loss of lubricant and high wear. The rigidity and coefficient of restitution of phenolic laminates are conducive to generating torque noise. The low porosity of only 2-10% in the phenolic laminates does not provide sufficient oil storage or safety margins for many critical applications. Also, the high wear rate of phenolic laminate due to its being a hard material leads to early failure of bearings in which it is employed.
More absorbent, sponge-like materials, such as felt, sponge rubber, or the like, have been found to be unsuitable for use in bearings. The oil transfer characteristics of oil impregnated material, such as felt, are not suitable for critical applications. Typically, during extended use, particles of the felt break off from the felt material, thus causing oil contamination and possible jamming of the bearing, resulting in bearing failure.
A retainer described in U.S. Pat. No. 4,073,552, issued Feb. 14, 1978, for Bearing Retainer and assigned to the assignee of the present invention has overcome most of the problems described above. This patent discloses using a soft, flexible, highly porous retainer material capable of absorbing between 40% and 80% by volume of a liquid lubricant, such as oil, and being capable of supplying 60% to 80% of the stored lubricant to the bearing. It also discloses that the retainer may be dimensioned so as to fit closely to the bearing balls and to the inner and outer races of the bearing. The clearance may be reduced compared to the clearance in conventional bearings by 50% to 75%. Conventional clearances between balls and pockets are usually on the order of 0.015 to 0.030 inches in a typical 6 inch diameter bearing having 5/8 inch diameter balls.
Although the clearances between the balls and the pockets and the retainer and the lands have been reduced substantially as compared to conventional bearings, these members are still free to vibrate or to change position with respect to one another which leads to torque noise and instability in the bearing.
The torque noise problem relates to both high frequency and low frequency torque noise. High frequency torque noise results when the bearing members are free to vibrate relative to one another at a frequency typically in the range of 50 to 100 Hz. The low frequency torque noise problem occurs when the viscous friction of the oil film on the bearing balls and races is not constant. The constantly changing thicknesses of the oil films at the various ball/retainer and land/retainer interfaces are caused by the changing relative position of the retainer with respect to bearing lands and balls. A making and breaking action occurs at the interfaces resulting in the low frequency torque noise occuring at a typical frequency of approximately 1/10 Hz.
Accordingly, it is an object of the present invention to provide a lubricating ball bearing retainer having a long useful life in critical applications where long duration and unattended operation is required.
Another object of the invention is the provision of a ball bearing retainer having low torque noise and a minimum of instability.
A further object of the present invention is the provision of a bearing retainer having a high oil storage capacity so that the oil will not become exhausted in a short time, and which is capable of supplying most of the stored oil to the bearing.